Bug 16741 - Remove dead code "sub itemissues" from C4/Circulation.pm

Bug 16741 - Remove dead code "sub itemissues" from C4/Circulation.pm

To verify:
- git grep itemissues
Result: Appears in C4/Circulation.pm only

To test:
- apply patch
- git grep itemissues
Expected result: No occurences
- prove t/db_dependent/Circulation.t
Expected result: Pass OK

Signed-off-by: Claire Gravely <c.gravely@arts.ac.uk>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>